[java] Intro openApiNullable property to enable/disable OpenAPI Jackson Nullable library (#6154)

* Add option to prevent usage of jackson-nullable (#2901)

Add a option for all java client and server to prevent
usage of third party library (jackson-databind-nullable)
which may be forbidden in some company

Add samples for Vertx, Spring MVC, Spring Cloud, Feign and Play

Upgrade dependencies for org.openapitools:jackson-databind-nullable

* Samples - Remove dependency org.openapitools:jackson-databind-nullable (#2901)

* Fix generation of gradle file for vertx (#2901)

* Regenerate samples (#2901)

* Fix documentation and up to date (#2901)

* Fix forgotten regeneration of vertx after dependency integration (#2901)

* Regenerate template after rebase (#2901)

* Use yaml config files introduce in #6509 to manage samples (#2901)

* Regenerate template using the config (#2901)

* Fix bad version during testing generated samples (#2901)

* Regenerate template after fix bad version (#2901)

* Fix merge, allow for set importing on codegen model

Co-authored-by: Jim Schubert <james.schubert@gmail.com>

samples/server/petstore/spring-mvc-j8-async/pom.xml

@@ -130,7 +130,7 @@
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
-            <version>0.1.0</version>
+            <version>${jackson-databind-nullable-version}</version>
         </dependency>
         <dependency>
             <groupId>junit</groupId>
@@ -164,5 +164,6 @@
         <jackson-threetenbp-version>2.8.4</jackson-threetenbp-version>
         <beanvalidation-version>1.1.0.Final</beanvalidation-version>
         <spring-version>4.3.20.RELEASE</spring-version>
+        <jackson-databind-nullable-version>0.2.1</jackson-databind-nullable-version>
     </properties>
 </project>

samples/server/petstore/spring-mvc-j8-async/src/main/java/org/openapitools/configuration/OpenAPIUiConfiguration.java

@@ -73,6 +73,7 @@ public class OpenAPIUiConfiguration extends WebMvcConfigurerAdapter {
         .indentOutput(true)
         .featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
         .modulesToInstall(new JsonNullableModule())
+        
         .dateFormat(new RFC3339DateFormat());
   }